The present invention relates to network based telephone systems and in particular to systems and methods of integrating a private branch exchange (PBX) into a shared resource network.
A network based PBX system is known from U.S. Pat. No. 5,875,234 which describes a computer integrated telephony system (CIT) that integrates a PBX with a Local Area Network (LAN). The PBX is connected to a server on a LAN. The PBX performs telecommunications functions which include establishing circuit connections between calls from a public telephone system and the individual extension lines of an office. If the connection to the server fails, the computer based PBX is able to maintain power. The known system uses a network element configured as a PBX. All call processing is carried out by the PBX, the server playing a non-existent or only a very minor role in the establishment of calls. An extension interface is provided on each PBX unit for addition of more PBX units to increase capacity. When this is done, one of the PBX""s is the master PBX and all others are in the normal mode. This known system does not exploit to the full the possibilities of distributed call processing and PBX facilities in a network. It does not provide a distributed PBX system integrated into a shared resource network such as a LAN.
It is an object of the present invention to provide a network based distributed PBX function and a method of operating the same which maintains calls during failure of the network or failure of the network""s server.
The present invention may provide a telecommunications system comprising: a shared resources network; an access module connected to the shared resources network for allowing telephone access to the telecommunications system; at least two user terminals connected to the access module; a call server on the shared resources network for controlling call signaling for each telephone call handled by the access module; wherein the access module is adapted to maintain a call between the two user terminals on the access module if connection to the call server is below a pre-determined quality of service. The access module is also preferably adapted to transfer the call signaling control back to the call server once the connection to the server is restored. On this switch back, all existing calls are maintained on the access module. Preferably, the access module has a means for continuously monitoring the quality of service of the connection to the call server. The monitor is used to decide whether the connection to the call server has been lost or restored and to take the necessary steps to switch to survival mode or to switch back to normal mode operation.
The present invention may also provide method of operating a telecommunications system having a shared resources network, an access module connected to the shared resources network for allowing telephone access to the telecommunications system; at least two user terminals connected to the access module; and a call server on the shared resources; the method comprising the steps of: using the call server to control call signaling for each telephone call handled by the access module in a first mode, establishing a call between the two user terminals connected to the access module; and when the connection between the access module and the call server drops below a pre-determined quality of service: maintaining the call between the two user terminals connected to the access module; and transferring control of call signaling to the access module from the call server for the call between the two user terminals.
The present invention may also provide a telecommunications system comprising: a shared resources network; a plurality of network elements connected to the shared resources network, the network elements comprising at least an access module for allowing telephone access to the telecommunications system and a call server for controlling call signaling for each telephone call handled by the access module; at least two user terminals connected to the access module; wherein the access module is configured to maintain a call between the two user terminals on the access module when call signaling control is transferred from the call server to another network element. The another network element may be another call server or the access module itself
The present invention may also provide method of operating a telecommunications system with a shared resources network and a plurality of network elements connected to the shared resources network, the network elements comprising at least an access module for allowing telephone access to the telecommunications system and a call server for controlling call signaling for each telephone call handled by the access module; establishing a call between at least two user terminals connected to the access module; maintaining the call between the two user terminals on the access module when call signaling control is transferred from the call server to another network element.
The present invention may provide a telecommunications system comprising: a shared resources network; an access module connected to the shared resources network for allowing telephone access to the telecommunications system; at least two user terminals connected to the access module; a call server on the shared resources network; wherein the access module is adapted to set up and maintain a call between the two user terminals on the access module if the connection to the call server is below a predetermined quality of service and for transferring call signaling control for each telephone call handled by the access module to the call server if connection to the call server is above a pre-determined quality of service.
The present invention may also provide a method of operating a telecommunications system having a shared resources network, an access module connected to the shared resources network for allowing telephone access to the telecommunications system; at least two user terminals connected to the access module; and a call server on the shared resources; the method comprising the steps of: using the access module to control call signaling for each telephone call handled by the access module in a first mode; establishing a call between the two user terminals connected to the access module; and when the connection between the access module and the call server rises above a pre-determined quality of service: maintaining the call between the two user terminals connected to the access module; and transferring control of call signaling to the call server from the access module for the call between the two user terminals.
The present invention may also provide an access module for a telecommunications system having a shared resources network and a call server in which the call server handles all call signaling; the module comprising: a monitoring unit for monitoring a quality of service parameter of a connection between the access module and the call server on the shared resources network, a management unit for deciding when the quality of service of the connection drops below a pre-determined level; and a switch over unit adapted for switching over the control of call signaling to the access module when the management unit decides that the connection with the call server is below the pre-determined quality of service.
Finally, the present invention may also provide an access module for a telecommunications system having a shared resources network and a call server as a network element; the module comprising: a monitoring unit for monitoring a quality of service parameter of a connection between the access module and the call server on the shared resources network, a management unit for deciding when the quality of service of the connection rises above a pre-determined level; and a switch over unit adapted for switching over the control of call signaling to the call server when the management unit decides that the connection with the call server is above the predetermined quality of service.
The present invention includes methods and apparatus for maintaining established local calls at an access module in case of change of the call control for a distributed PBX over a communications network, e.g. WAN or LAN, especially an IP network. This will be described for two different embodiments of the present invention. In accordance with the first main embodiment, the system is composed of one Call Server controlling the call processing of other PBX access modules in a normal situation. The access modules will be described as operating in Normal mode in this case. These access modules have the ability to operate in Stand Alone or Survival mode if the link (connection) to Call Server is down for any reason. In the second main embodiment, two call servers may be used, an active call server and a hot-standby server. The active call server controls the call processing of the access modules. In case the link (connection) between one access module and the active call server fails, the hot-standby Call Server can take over the control of the access module. Therefore, each module can operate in normal mode of the active call server 1 or in normal mode of the hot-standby call server or, as an alternative to either of these, in stand alone or survival mode.
The dependent claims define separate, individual embodiments of the present invention. The present invention will now be described with reference to the following drawings.